We have lots of very successful friends. Mostly, because DH did the Eton-Oxford-Bar thing, and I went to a high performing girls' school and UCL (but then into a more diverse, if competitive, profession).
While several of our successful male friends did go to 'top' schools, most went to decent comps, grammar schools or day schools. Not one of the professionally very successful women I know, either at work or personally went to a posh girls' boarding schools (I did have a university tutor expelled from Rodean in 1964), although many went to GDST schools or grammars. We've chosen a small independent day school for DD, and then she'll go to the local grammar sixth form.
A disproportionate number of DH and his brothers' old Eton pals are vaguely in PR, professional pilgrims or eternally writing a novel. Several are carpenters. Which I guess is another way to be in the cabinet.
We were reflecting the other day that none of our friends, even those who were at Eton, Charterhouse etc. are sending their kids away to traditional boarding schools. Mostly primary/ cosy prep and then onto independent day schools. I know one lady who has sent her child to Harrow. Both parents went to state schools, and she is a dedicated social climber. Noone else seems to feel it's a good choice nowadays, and I agree.